The holotype of Minmi paravertebra was discovered by Alan
Bartholomai near
Roma, Queensland, in 1964, and described by
Ralph Molnar in 1980. The partially articulated remains consisted
of eleven thorasic vertebrae with ribs, most of the ventral body
armour and an incomplete hind foot. In 1990 another specimen was
discovered on Marathon Station, Queensland, which has been designated as
a Minmi sp. This specimen was almost complete, lacking only
the right ilium, distal (lower) parts of the left limbs, and the
distal end of the tail. It also included most of the body armour, consisting
of large and small scutes on the body, large scutes on the limbs,
plates around the neck, tear-drop shaped spiked plates behind the
hips, and triangular plates and large scutes along the tail.
The Marathon specimen, as well as a third partial
ankylosaur found nearby, are yet to be completely prepared.
At least five other individual fragments in the Queensland Museum
have also been tentatively referred to Minmi, two of
which may come from the same individual animal.

The holotype included two features unusual to ankylosaurs.
The vertebrae had bony projections along side the neural spines
called paravertebrae (hence the species name) which seem to be unique
among dinosaurs. These seem to be ossified tendons rather than bones
in their own right, and it may be that such tendons have simply
not been preserved in other ankylosaurs, perhaps because only in Minmi
were the tendons ossified to form bone.
The other unique feature is seen in skin impressions of the belly skin,
which show that even the underside was protected by small bony
scutes imbedded in the skin. Most thyreophorans ("shield bearers",
the group that includes ankylosaurs, nodosaurs, stegosaurs, and primitive
ancestoral forms) lacked armour on the belly.

One theory concerning the function of the paravertebrae suggests
that they helped to reinforce the back and bear the weight of the
armour to allow the creature to run. Given the small size (around 3
metres long) of the specimen, and the relatively long legs for an
ankylosaur, this theory would make sense. Most ankylosaurs would have
been too large and heavily armoured to have been able to run at any great
speed. The structure of the paravertebrae in Minmi is similar to
the tendons seen in the vertebrae of crocodilians, which serve to stiffen
the croc's back so they can "gallop" like a rabbit when they are young
(see the background image on the Australian Dinosaur
Fossils page, based on a photo of a fresh water crocodile galloping).

The exact relationship between Minmi and other armored dinosaurs is uncertain.
It seems to exhibit characteristics of both ankylosaurs and nodosaurs.
Minmi has a long postacetabular region of the illium similar to
that of scelidosaurs, whereas in ankylosaurs and stegosaurs it is much shorter.
The region of the snout arches higher than the roof of the skull, a feature seen
in nodosaurs. The pattern of the bones that make up the skull are more similar
again to scelidosaurs than either ankylosaurs or nodosaurs. The femora of most
ankylosaurs are flattened fore and aft, whereas the femur of Minmi is
rounded in cross section, more like those of the ancestral thyreophorans.
Minmi may turn out to be closer to ankylosaurs than to nodosaurs,
although if so it seems to have split off from
them early in their evolution. Similar Minmi-like material from New Zealand suggests
that Minmi itself probably did not have a tail club, which is a feature common to
almost all other Ankylosaurs.

If you had to design a creature that had to contend with velociraptors on
a regular basis you might come up with something similar to Minmi.
The armoured belly may have given them some protection from sharp
retractable foot claws. The body armour lay mostly between the ribs, and
if this was not an artefact of preservation then they too may have helped
to ward off foot-claw attacks. The blade-like cross section of dromaeosaur
sickle claws would have been well designed to slice between the ribs of
prey to damage the internal organs. But of all the defences
the best would have been to run away, since dromaeosaur were probably
not as fast as most theropods. This is all speculation on my part of
course. The spikes along the hips and tail
would have prevented a small predator from leaping onto the hind
quarters to slow the Minmi down, and may have discouraged
attacks from above by larger predators.